dart / co19 / ec3903d67de5f63200bb83cfa7c9f3e9fdd9c7bc / . / LanguageFeatures / Super-bounded-types / static_analysis_A01_t08.dart

// Copyright (c) 2018, the Dart project authors. Please see the AUTHORS file | |

// for details. All rights reserved. Use of this source code is governed by a | |

// BSD-style license that can be found in the LICENSE file. | |

/// @assertion We say that the parameterized type G<T1..Tk> is regular-bounded | |

/// when Tj <: [T1/X1 .. Tk/Xk]Bj for all j, 1 <= j <= k, where X1..Xk are the | |

/// formal type parameters of G in declaration order, and B1..Bk are the | |

/// corresponding upper bounds. | |

/// This means that each actual type argument satisfies the declared upper bound | |

/// for the corresponding formal type parameter. | |

/// We extend covariance for generic class types such that it can be used also in | |

/// cases where a type argument violates the corresponding bound. | |

/// For instance, assuming the classes [C] and [D] as declared in the | |

/// [Motivation] section, [C<D>] is a subtype of [C<Object>]. This is new because | |

/// [C<Object>] used to be a compile-time error, which means that no questions | |

/// could be asked about its properties. Note that this is a straightforward | |

/// application of the usual covariance rule: [C<D> <: C<Object>] because | |

/// [D <: Object]. We need this relaxation of the rules in order to be able to | |

/// define which violations of the declared bounds are admissible. | |

/// @description Checks that assigning [Object] as a bound of super-bounded type | |

/// does not cause compile error in case of several type parameters. | |

/// @author iarkh@unipro.ru | |

/// @issue #32903 | |

class C<X extends C<X, Y>, Y extends C<X, Y>> {} | |

class D extends C<D, D> {} | |

main() { | |

D d = new D(); | |

C<Object?, Object?> c = d; | |

dynamic c2 = d; | |

} |